Hepatic fibrosis and the granulomatous response to eggs of schistosome species pathogenic for man are studies in mice in relation to parasitologic parameters of infection. Treatment of mice with anti-IL-5 monoclonal antibody depleted S. japonicum infected mice of eosinophils. Granulomas without eosinophils were only slightly reduced in size and had fibrosis equivalent to that in untreated mice. Splenic lymphocytes from S. japonicum infected animals secrete IL-5 but not interferon tau after stimulation with egg antigen or ConA. These findings parallel the reactions examined previously in S. mansoni infected mice and suggest the importance of Th-2 cells, but not IL-5, for the formation of granulomas and the development of fibrosis in murine S.japonicum infection.